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How to group equal values in J?

   (= <@#"1 0 ~.) 3 2 3 3 4
+-----+-+-+
|3 3 3|2|4|
+-----+-+-+

What other ways are there? I mostly don’t like the part where it says "1 0.

Solution

  • The adverb key (/.) groups the right argument as specified by the left argument and applies a verb to each group. If you give it the same left and right argument you can apply the verb box (<) to group all the equal items 

       </.~ 3 2 3 3 4
┌─────┬─┬─┐
│3 3 3│2│4│
└─────┴─┴─┘

    You could easily sum the groups instead:

       +//.~ 3 2 3 3 4
9 2 4